Shielding arrangements for vacuum-type circuit interrupters of the two-contact type

ABSTRACT

A vacuum-type circuit interrupter of the two-contact type is provided with a short shield for preventing the deposition of metallic vapor from the arcing region upon the inner surfaces of the outer insulating casing of the vacuum-type circuit interrupter. For certain applications, the shield is made of considerable thickness to enable it to withstand the heavy arcing, which may occur thereat. In addition, for other applications, the short shield may be formed of an electrode-type material so that arcing may occur without damage to the shield.

United States Patent [72] inventor Werner S. Emmerich Pittsburgh, Pa.

[21] Appl. No. 789,981

[22] Filed Jan. 9, 1969 [45] Patented Oct.12, 1971 [73] AssigneeWestinghouse Electric Corporation Pittsburgh, Pa.

[54] SHIELDING ARRANGEMENTS FOR VACUUM- TYPE CIRCUIT INTERRUPTERS OF THETWO- CONTACT TYPE 7 Claims, 11 Drawing Figs.

[52] US. Cl 200/144 B [51] ...,...H0lh 33/66 [56] References CitedUNITED STATES PATENTS 2,900,476 8/1959 Reece 200/144 (.2)

3,185,800 5/1965 Titus .t 200/144 (.2)

3,189,715 6/1965 Jennings 200/144 (.2)

Ila

3,372,2583/1968 Porter "Zoo 144 2 3,470,341 9/1969 BeddOC zoo 144 2FOREIGN PATENTS 1,230,339 9/1960 France zoo 144 2 379,342 8/1932Gl'CaIBl'llfilil. zoo 144 2 213,123 12/1968 U.S.S.R. zoo 144 2 PrimaryExaminer-David Smith, Jr.

Assistant Examiner-Robert A. Vanderhye Attorneys-A. T. Stratton, ClementL. McHale and Willard R.

Crout Ilb PATENTEDucT 12 I97! Ila u FIG.6

. m 6 am .F m

CW I m m ,0 n m 2 F 3 m u w m PRIOR ART INVEN'IIOR Werner S. Emmerlch BYj 66' M P. M W ATTORNEY SHIELDING ARRANGEMENTS FOR VACUUM-TYPE CIRCUITINTERRUPTERS OF THE TWO-CONTACT TYPE BACKGROUND OF THE INVENTION Most ofthe metallic vapor emanating from the electrode region in a vacuuminterrupter deposits upon the vapor shield in a relatively narrow bandextending not much beyond the open space between the electrodes. If, forinstance, the electrode spacing is one-half inch, a shield length of 1%inches, extending one-half inch on either side, would catch most of thevapor. Not only that, but any vapor particles striking a shield beyondthat distance are not likely to be scattered into a space, where theycould be detrimental to the interrupting capability of the circuitbreaker. For example, the shield described in US Pat. No. 3,048,681,issued Aug. 7, 1962 to George Polinko, Jr. is typical of such types oflong metallic shields of the prior art. Another patent, which istypical, is Veras US Pat. No. 3,048,682, issued Aug. 7, 1962.

SUMMARY OF THE INVENTION In accordance with preferred embodiments of thepresent invention, it is proposed to provide a narrow special shieldincorporated into the vacuum circuit-interrupter geometry of thetwo-contact type. This shield is to be made of well-out gassed metal andsufficiently thick so as to have maximum effectiveness in catchingmetallic vapor emitted from the electrode region. The material chosenshould also be one for which the sticking probability is naturally good,that is, it welds easily with the electrode material.

In accordance with particular embodiments of the invention, the shortshield may be backed up by other shields, either metallic, ornonmetallic, of arbitrary thickness, whose only function is to shieldthe insulator against residual metallic vapor from the arc. Such shieldscould be mounted on the insulators, on the end plates, or on theelectrode stems.

In accordance with another embodiment of the present invention, theauxiliary shield is of such thickness that it constitutes an auxiliaryelectrode, to which arcing may occur, and thus constitute a circuitinterrupter which establishes two arcs in series.

Still further embodiments of the present invention involve a shieldingarrangement in which the shield material is formed of an electrode-typematerial, so that erosion thereat may be maintained at a minimum.

Accordingly, it is a general object of the present invention to providean improved vacuum-type circuit interrupter of the two-contact typehaving an improved shielding arrangement.

Another object of the present invention is the provision of an improvedvacuum-type circuit interrupter in which the shield is of minimum axiallength.

Another object of the present invention is the provision of an improvedshielding arrangement for a vacuum-type circuit interrupter in which theshield may constitute an auxiliary electrode in which two arcs are drawnthereat during a normal operation of the interrupter.

Still a further object of the present invention is the provision of animproved vacuum-type circuit interrupter in which the short shield isformed of a suitable electrode material to prevent arc erosion, and toconstitute auxiliary electrode means.

Further objects and advantages will readily become apparent upon readingthe following specification, taken in conjunction with the drawing.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross'sectional view of avacuum-type circuit interrupter of the two-contact type embodying theinvention in one form;

FIGS. 2-5 illustrate modifications of the short vapor shield of thepresent invention;

FIGS. 69 illustrate variants of the shield construction of 1 FIGS. 1-5except that the short vapor shield is of sufficient thickness so as tobe capable of withstanding arcing;

FIG. 10 illustrates a modification of the invention in which the shortshield is made of an electrode material; and,

FIG. 11 illustrates a phenomenon which has been observed to occur duringcircuit interruption in prior art structures.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to theinterrupter of FIG. 1, there is shown a highly evacuated envelope 10comprising a tubular casing 11 of insulating material, such as asuitable glass, and a pair of metallic end caps 12 and 13 closing offthe ends of the casing. Suitable seals 14 are provided between the endcaps and the casing to render the envelope [0 vacuumtight.

Located within the envelope is a pair of separable electrodes, or rodcontacts 17 and 18, shown by solid lines in the open-circuit position.The electrode 17 is a stationary electrode suitably united to the endcap 12, whereas the electrode 18 is a movable electrode suitably mountedfor reciprocal movement, and projecting through an opening in the endcap 13. A flexible metallic bellows 20, interposed between the end cap13 and the movable electrode 18, provides a seal about the removableelectrode, and allows for reciprocal movement thereof without impairingthe vacuum inside the interrupter. As shown on the drawing, the bellows20 is sealingly secured at its respective opposite ends to the electrode18 and to the end cap 13.

Coupled to the end of the movable electrode 18, I provide suitableactuating means (not shown), which is capable of driving the electroderapidly inwardly from its solid-line position of FIG. I to itsdotted-line position to close the interrupter, and which is also capableof returning the electrode to the solid-line position to open theinterrupter.

When the electrode is driven outwardly to open the interrupter, acircuit-interrupting, or arcing gap is established between the adjacentends of the electrodes, and the resulting are, though quicklyextinguished, vaporizes some of the metal constituting the electrodes.

In order to prevent this metallic vapor from condensing on the internalinsulating surfaces 11a of the casing 11, there is provided a shortmetallic shield 25. This short metallic shield 25 is of a generallytubular configuration, and extends along the length of the casing 11 foronly a short distance. The shield 25 is electrically isolated from bothof the electrodes 17 and 18 and, preferably, is also isolated fromground; or in other words, the shield is at a floating potentialrelative to the two electrodes l7, l8.

This electrical isolation between the shield 25 and the electrodes l7and 18 is achieved by mounting the shield 25 on the insulating casing 11adjacent the central region of the shield, as at 1112, and by spacingthe short shield 25 radially inwardly from the tubular insulating casing11 at all points on opposite sides of the centrally disposed mountingregion.

I have discovered that the metallic vapor emanating from the electroderegion 9 is a vacuum-type circuit interrupter deposits on the vaporshield in a relatively narrow band extending not much beyond the openspace between the electrodes. If, for instance, the electrode spacing 9is one-half inch, a shield length of lkinches, extending one-half inchon either side, would catch most of the emitted metallic vapor. Not onlythat, but any vapor particles striking a shield beyond that distance arenot likely to be scattered into a space, where they could be detrimentalto the interrupting capability of the circuit breaker.

It is, therefore, an objective of the present invention to provide aspecial narrow shield 25 incorporated into the geometry of thevacuum-type circuit interrupter. This shield 25 is preferably made fromwell-outgassed metal, and sufficiently thick so as to have maximumeffectiveness in catching metallic vapor emitted from the electroderegion 9. The material chosen should also be one for which the stickingprobability is naturally good, that is, it welds easily with theelectrode material l7, 18. Such preferable materials are metals andalloys having a vapor pressure lower than magnesium but are not asrefractory as tungsten. Nickel, copper, silver and stainless steel areexamples of suitable materials which may be used.

The short shield 25 may be backed up by other shields, either metallicor nonmetallic of arbitrary thickness, whose only function is to shieldthe insulator 11 against residual metallic vapors from the arc. Suchshields may be mounted on the insulator 11, on the end plates 12, 13, oron the electrode stems 17a, 18a, as shown in FIGS. 2-5 of the drawings.

With reference to FIG. 2, it will be observed that an outer backupshield 30 is provided together with end metallic shields 31, 32connected, respectively, to the electrode stems 17a, 18a.

FIG. 3 illustrates a modified construction in which the relatively shortcentral shield 25a has inwardly extending end portions 25b, 25c toassist in confining the metallic vapor emitted from the arcing region 9.As in the construction of FIG. 2, end metallic shields 31, 32 areprovided fixedly attached to the electrode stems 17a, 18a.

FIG. 4 illustrates a construction in which the relatively short centralvapor shield 25 has cooperating therewith end metallic shields 40, 41,which are attached, respectively, to the electrode stems 17a, 18a andcurve inwardly.

FIG. 5 shows a modified arrangement in which the short shield 25a hasinwardly extending end portions 25b, 25c, and the end shields 33, 34project inwardly from the end plates 12, 13 of the interrupter.

It has been found that during very high-current arcing, breakdown mayoccur to the shield entailing currents of sufficient magnitude to meltholes in the shield according to prior arrangements, as shown in FIG.11. If the short shield 25 is manufactured of sufficient thickness tonot only withstand the normal vapor deposition, but also able towithstand arcing, then such failures cannot occur. In fact, arcing tothe short shield 25 can be tolerated in the normal operation of theinterrupter, and the short shield is, in fact, an auxiliary short shieldelectrode.

FIGS. 6-10 illustrate modifications of FIGS. 1-5 with the exception thatthe short shields 25 are of considerable thickness, as is evident froman inspection of the figures. Thus the short shields can tolerate theheavy-current arcing, which, in fact, may exist.

It will be noted that in the construction set forth in FIG. 7 of thedrawings, the end metallic shields 33a, 34a are again fixedly attachedto the end metallic plates 12, 13. However, the inner adjacent ends ofthe end shields have an enlarged peripheral portion, such as provided bya spinning operation, for example, to enlarge the radius of curvature tothereby reduce the electrical field gradient. Again the end shields 31,32 may be additionally used, as shown.

Many experiments emphasize the destructive arcing that can occur betweenelectrodes by way of the central shield of a vacuum interrupter, eventhough the spacing is such that arcing is not expected. It is believedthat this arcing can take place because of two simultaneous phenomena.One is the preferential motion of the arc toward the shield by magneticfields set up from the current flowing in the electrodes and externalcircuitry. The other reason is that when the interrupter is in thehigh-current mode of arcing, voltage spikes of sufficient height areobserved to tolerate the existence of a doublegap are.

As a further modification of the invention, and to take advantage ofsuch a situation, such as the foregoing, there is provided an auxiliarycentral cylindrical electrode 50 for the specific purpose of handlinethis type of a discharge. FIG. 10 illustrates an electrode geometrycapable of supporting a double-gap arc without damage. This structure issimilar to that previously described, but the essential difference isthat in FIG. 10, the central auxiliary electrode 50 is made of anelectrode-type material, so that arcing may occur without damage to theshield. In other words, the central auxiliary electrode 50 is made ofthe same type of contact material, and capable of withstanding erosion,as the separable main contacts 17, 18 of the circuit-interruptingdevice. As examples of suitable electrode materials which may be used, acopper-silver alloy may be employed, or the electrode material set forthin U.S. Pat. application filed May 29, 1967, Ser. No. 64l,88l nowabandoned by Alfred Alexander Robinson may be used. This is a materialcomprising a matrix of chromium, cobalt, nickel or iron infiltrated witha second metal, such as copper, copper alloy, silver or a silver alloy,or an alloy of copper and zirconium, tantalum or titanium, as set forthin the aforesaid application, Ser. No. 641,881.

From the foregoing description of the invention it will be apparent thatthere have been provided short novel shielding arrangements forpreventing the deposition of metallic vapor on the inner walls 11a ofthe outer insulating casing 11, and additionally, providing adouble-break type of circuit interrupter (FIG. 10). By the provision ofthe relatively short central shield 48 of adequate thickness to serve asan auxiliary electrode, or by even fabricating the relatively shortshield of electrode material 50 (FIG. 10) to withstand erosion, a highlyefficient and simplified type of vacuum circuit interrupter is providedhaving considerable voltage-interrupting power.

Although there have been illustrated and described specific structures,it is to be clearly understood that the same were merely for the purposeof illustration, and that changes and modifications may be readily madetherein by those skilled in the art, without departing from the spiritand scope of the invention.

lclaim:

l. A vacuum-type circuit interrupter of the two-contact type comprising,in combination:

a. an outer evacuated tubular casing of insulating material;

b. a pair of contacts disposed within said evacuated casing andseparable to establish an arc;

c. said contacts when in the fully open-circuit position defining a gapseparation distance 0 s";

d. a generally tubular short vapor-condensing metallic shieldsurrounding the arcing region and of a relatively short axial length ofapproximately 3s";

e. the vapor-condensing shield being spaced radially inwardly of theinner wall of the outer tubular casing and close to the separatecontacts;

f. the vapor-condensing shield being at a floating electrical potentialand not electrically connected to either of the separable contacts; and,

g. said short shield having its ends curved inwardly toward the contactsto confine the metallic vapor emitted from the arcing region.

2. The combination of claim 1, wherein the shield is of heavy sheetmaterial.

3. The combination of claim 1, wherein the shield is fabricated ofelectrode material.

4. The combination of claim 1, wherein a pair of tubular end shieldextend axially inwardly from the metallic end plates of the evacuatedenvelope and are supported thereby.

5. The combination of claim 4, wherein the confronting facing inner endsof the end shields are rolled to form a large radius of curvature thereat to thereby reduce the electrical field strength.

6. The combination of claim 1, wherein a pair of end shields are securedto the contact rods.

7. A vacuum-type circuit interrupter comprising, in combination:

a. an outer evacuated tubular casing of insulating material;

b. a pair of contacts disposed within said evacuated casing andseparable to establish an arc;

c. said contacts when in the fully open-circuit position defining a gapseparation distance of s;

d. a generally tubular short vapor-condensing metallic shieldsurrounding the arcing region and of a relatively short axial length ofapproximately 3s;

e. the vapor-condensing shield being spaced radially inwardly of theinner wall of the outer tubular casing;

f. the vapor-condensing shield being at a floating electrical potentialand not electrically connected to either of the separable contacts;

tioned shield; and, j. said backup shield being of greater axial lengththan the inner short shield.

1. A vacuum-type circuit interrupter of the two-contact type comprising, in combination: a. an outer evacuated tubular casing of insulating material; b. a pair of contacts disposed within said evacuated casing and separable to establish an arc; c. said contacts when in the fully open-circuit position defining a gap separation distance of ''''s''''; d. a generally tubular short vapor-condensing metallic shield surrounding the arcing region and of a relatively short axial length of approximately ''''3s''''; e. the vapor-condensing shield being spaced radially inwardly of the inner wall of the outer tubular casing and close to the separate contacts; f. the vapor-condensing shield being at a floating electrical potential and not electrically connected to either of the separable contacts; and, g. said short shield having its eNds curved inwardly toward the contacts to confine the metallic vapor emitted from the arcing region.
 2. The combination of claim 1, wherein the shield is of heavy sheet material.
 3. The combination of claim 1, wherein the shield is fabricated of electrode material.
 4. The combination of claim 1, wherein a pair of tubular end shield extend axially inwardly from the metallic end plates of the evacuated envelope and are supported thereby.
 5. The combination of claim 4, wherein the confronting facing inner ends of the end shields are rolled to form a large radius of curvature there at to thereby reduce the electrical field strength.
 6. The combination of claim 1, wherein a pair of end shields are secured to the contact rods.
 7. A vacuum-type circuit interrupter comprising, in combination: a. an outer evacuated tubular casing of insulating material; b. a pair of contacts disposed within said evacuated casing and separable to establish an arc; c. said contacts when in the fully open-circuit position defining a gap separation distance of s''''; d. a generally tubular short vapor-condensing metallic shield surrounding the arcing region and of a relatively short axial length of approximately 3s; e. the vapor-condensing shield being spaced radially inwardly of the inner wall of the outer tubular casing; f. the vapor-condensing shield being at a floating electrical potential and not electrically connected to either of the separable contacts; g. said short shield having its ends curved inwardly toward the contacts to confine the metallic vapor emitted from the arcing region; h. a backup shield disposed outwardly of said first-mentioned shield; and, j. said backup shield being of greater axial length than the inner short shield. 